The present invention relates to a wrench, which comprises a hollow casing having multiple ends, a plurality of coupling shafts respectively mounted in the ends of the casing to hold a respective tool accessory for synchronous rotation, and a transmission mechanism coupled between the coupling shafts for enabling the coupling shafts to be synchronously rotated.
Various wrenches have been dislcosed, and have appeared on the market. FIG. 1 shows a wrench, which comprises a hollow two-way casing, two coupling shafts respectively mounted in the two ends of the casing for holding a respective tool accessory. The coupling shafts each have an inner end meshed together by means of a respective bevel gear for synchronous rotation. This structure of wrench is still not satisfactory in function. Because lubricating grease can not be applied to the bevel gears, the teeth of the bevel gears wear quickly with use. When the teeth of the bevel gears start to wear, driving power can not be positively transmitted from one coupling shaft to the other.
The present invention provides a wrench, which eliminates the aforesaid drawbacks. According to one aspect of the present invention, the wrench comprises a hollow three-way (or two-way) casing, a plurality of coupling shafts respectively mounted in the ends of the casing for holding a respective tool accessory, and a transmission mechanism coupled between the coupling shafts for enabling the coupling shafts to be rotated synchronously. The transmission mechanism comprises a plurality of transmission members respectively coupled to the coupling shafts inside the casing and meshed with one another, and a plurality of compression springs respectively mounted in the coupling shafts to force the transmission members into engagement with one another. The transmission members each have a rectangular shank at one end inserted into a rectangular coupling hole on the respective coupling shaft and supported on the corresponding compression spring, and a bevel gear at an opposite end meshed with the bevel gear at the trasmission member in an adjacent coupling shaft. According to another aspect of the present invention, lubricating grease is applied to the bevel gears of the transmission members.